This invention relates generally to semiconductor protection circuitry and more particularly, it relates to a protection circuit for semiconductor integrated circuits having bipolar transistors to prevent inadvertent damage caused by electrostatic discharge (ESD) occurring between any two of the external connector terminals or pins of an integrated circuit package.
Generally, ESD protection circuitry of the prior art consisted of a small diode, a Zener diode or a transistor connected between either an input pin or an output pin and a power supply pin. These prior art ESD protection circuitry had the drawback of being unable to handle large currents. Another drawback is that the prior art protection circuits offered protection to the input or output pin only when the power supply pin was made to come in contact with a ground potential. Thus, these prior art protection circuits offered no protection when another input or output pin was the one referenced to ground. Further, no discharge path existed when the ESD occurred at the power supply pin.
Since the build-up of such electrostatic charges could be applied typically during handling to any one of the plurality of external connector terminals or pins of the integrated circuit package, a discharging occurs when any one of the remaining pins comes into contact with the ground potential. As a consequence, the discharging could occur, in essence, between any one of the external pins and any one of the other remaining pins.
It is also known that thyristors are generally useful as ESD protection structures due to their ability to handle large amounts of power. In particular, the thyristors have the characteristic of being able to hold off high voltage at low reverse current in the blocking state but yet can conduct high currents with low voltage drops in the forward conduction state. The use of thyristors as protection devices is discussed in a published article entitled "Using SCR's As Transient Protection Structures in Integrated Circuits" by L. R. Avery, RCA DSRC, pages 177-180. However, the article by Avery teaches only the use of two thyristors for protection against both positive and negative transients.
It would therefore be desirable to provide a protection circuit for semiconductor integrated circuits having bipolar transistors to prevent inadvertent damage caused by electrostatic discharge occurring between any pin and any other remaining pin of the integrated circit package. The protection circuit of the present invention includes a plurality of clamping networks. Each of the clamping networks includes a single thyristor and a single diode connected between each external input/output pin and an external substrate pin of the integrated circuit package.